Two figures are similar if they have the same shape.

Two figures are congruent if they have both the same shape and the same size.

All congruent figures are similar. Only similar figures which are also the same size are congruent.

The figures below are similar. The figures below are NOT congruent. Although they are the same shape, they are all different in size.

All of the figures below are congruent since they all have the same shape and size. Since they are all congruent, they are as a result all similar.

The two figures below are neither similar nor congrent since they do not have the same shape.